1. Field of the Invention
The disclosed embodiments of the present invention relate to voltage reference generation mechanism, and more particularly, to a voltage reference generation circuit with a low temperature coefficient, low line regulation and/or a wideband high power supply rejection ratio, and related voltage reference generation method, voltage regulation circuit and voltage regulation method.
2. Description of the Prior Art
In order to design a voltage reference generation circuit with a lower temperature coefficient, a bipolar junction transistor (BJT), a diode, and a depletion-mode metal-oxide-semiconductor field effect transistor (MOSFET) are usually used for temperature compensation. For example, a BJT is used in a conventional bandgap voltage reference circuit for temperature compensation. As it is expensive to fabricate a BJT with a bipolar complementary metal-oxide-semiconductor (BiCMOS) process, the parasitic effect of the standard complementary metal-oxide-semiconductor (CMOS) process is commonly used for BJT fabrication. However, because a base of the fabricated parasitic BJT has to be connected to ground and occupies a large area, the voltage reference circuit fabricated with the above process may have limited application.
Please refer to FIG. 1, which is a diagram illustrating a partial circuit of a conventional voltage reference generation circuit. The voltage reference generation circuit 100 includes a current supply circuit 110 and a core circuit 120. The current supply circuit 110 includes a plurality of MOSFETs M1-M5 and a resistor R1, and is arranged to provide a current to the core circuit 120. The core circuit 120 includes a plurality of MOSFETs M6-M7 and a plurality of resistors R2-R3, and is arranged to generate a voltage reference V_REF by using the resistors R2-R3 and temperature dependences of the MOSFETs M6-M7. However, the voltage reference generation circuit 100 needs at least three current paths (i.e. respective flow paths of currents I1-I3), and a power supply rejection ratio (PSRR) of the voltage reference generation circuit 100 is reduced due to the resistors R2 and R3. Thus, not only does the voltage reference generation circuit 100 consume more energy, but the variation of the voltage reference V_REF due to a power supply VDD will be apparent.
In order to enhance a PSRR of a voltage reference generation circuit, a core circuit of the voltage reference generation circuit is usually connected to a pre-regulator circuit. Please refer to FIG. 2, which is a diagram illustrating a partial circuit of another conventional voltage reference generation circuit. The voltage reference generation circuit 200 includes a plurality of MOSFETs M1-M18, a plurality of BJTs Q1-Q5, and a plurality of resistors R1 and R2, wherein the voltage reference generation circuit 200 is arranged to generate a regulated voltage V_REG by using a pre-regulator circuit, and accordingly suppress disturbance (from a power supply VDD) in a voltage reference V_REF. By analyzing the circuit shown in FIG. 2, a person skilled in the art can find that lots of transistors are needed, and positive and negative feedback effects are generated simultaneously in the voltage reference generation circuit 200. Thus, the circuit needs to be modified to make the positive feedback effect weaker than the negative one. In addition, when the voltage reference generation circuit 200 operates at a higher operation frequency, the PSRR would be greatly reduced, resulting in limited wideband application of the voltage reference generation circuit 200.
Please refer to FIG. 3, which is a diagram illustrating a partial circuit of another conventional voltage reference generation circuit. The voltage reference generation circuit 300 includes a plurality of MOSFETs M1-M12, a resistor R1 and a plurality of capacitors C1 and C2. The circuit architecture shown in FIG. 3 may enhance the PSRR of the voltage reference generation circuit 300 and reduce the number of used transistors. Unfortunately, the voltage reference generation circuit 300 exhibits higher sensitivity to temperature variations. Moreover, each of the voltage reference generation circuits 100-300 shown in FIGS. 1-3 may generate a body effect, which changes a corresponding threshold voltage.
Thus, how to implement a voltage reference generation circuit having a low temperature coefficient, a high PSRR, low fabrication cost and a weak body effect is a problem that needs to be solved.